Experimental Study on Back-Flushing Characteristics of an In-Vessel Filtration System in Fischer–Tropsch Slurry Reactors

Abstract

An in-vessel filtration system is a crucial component in commercial low-temperature Fischer–Tropsch slurry reactors for the continuous separation of liquid products and catalysts generated by the reaction. Periodic back-flushing is key to ensuring the stability and continuity of the in-vessel filtration system, but it has been relatively unexplored. In this study, systematically and experimentally, the back-flushing characteristics of in-vessel filtration are investigated, including the characteristics of the back-flushing process, the influence of back-flushing conditions on the recovery of filtration performance, and some inherent issues for back-flushing. The results indicate that the in-vessel filtration back-flushing process exhibits four typical stages: pre-back-flushing stage I, back-flushing stage II, back-flushing buffering stage III, and reuse stage IV. In stage II, the process lasts longer due to the incompressibility of the liquid, and it also has a certain entrainment effect on particles. In stage III, the remaining liquid level after liquid back-flushing can inhibit the inflow of liquid, partially preventing a premature decline in filtration performance. As a result, the recovery of filtration performance following liquid back-flushing is superior to that of gas. There exists a threshold value for both gas and liquid back-flushing differential pressures, beyond which there is no significant improvement in filtration performance. The recovery of filtration performance varies significantly along the filter tube height due to differences in flow resistance. During gas back-flushing, the impact of high-pressure gas on the bed causes significant pressure fluctuations, affecting the operational stability of the slurry reactor. Residual particles that cannot be fully removed by back-flushing exist in the filter tube gaps, and their gradual accumulation is one of the main causes of filter failure. These findings contribute to a better understanding of in-vessel filtration back-flushing and help in the development of improved back-flushing schemes for industrial plants.